From: Josh Cheek <josh.cheek@...>
Date: 2010-11-08T17:52:01+09:00
Subject: Re: Don't work an array

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On Sun, Nov 7, 2010 at 5:00 PM, Misha Ognev <b1368810@lhsdv.com> wrote:

> Hello, this don't work on ruby 1.9.2. What's matter?
>
> $a = Array.new
> for i in 1..5
>  for j in 1..8
>    $a[i][j] = i*j
>  end
> end
>
> --
> Posted via http://www.ruby-forum.com/.
>
>
The problem is that you haven't initialized the indexes you are accessing.

$a = Array.new
for i in 1..5
  $a[i] = Array.new # **initialize**
  for j in 1..8
    $a[i][j] = i*j
  end
end




Of course, you have several other issues as well. In Ruby, variables
beginning with dollar signs are global. That is probably not what you wanted
to do. To make it a local var, just don't use a sigil.

a = Array.new # now it is local
for i in 1..5
  a[i] = Array.new
  for j in 1..8
    a[i][j] = i*j
  end
end




You still have the issue that your array begins at 1, but Ruby arrays begin
at zero. This means your first index is left nil. You can see what your
object looks like by requiring the pp library, and passing a to the pp
method.

require 'pp'
pp a
# >> [nil,
# >>  [nil, 1, 2, 3, 4, 5, 6, 7, 8],
# >>  [nil, 2, 4, 6, 8, 10, 12, 14, 16],
# >>  [nil, 3, 6, 9, 12, 15, 18, 21, 24],
# >>  [nil, 4, 8, 12, 16, 20, 24, 28, 32],
# >>  [nil, 5, 10, 15, 20, 25, 30, 35, 40]]




That probably isn't what you wanted. As stated by other users, check out the
block form of Array.new

require 'pp'

a = Array.new 5 do |i|
  Array.new 8 do |j|
    i * j
  end
end

pp a
# >> [[0, 0, 0, 0, 0, 0, 0, 0],
# >>  [0, 1, 2, 3, 4, 5, 6, 7],
# >>  [0, 2, 4, 6, 8, 10, 12, 14],
# >>  [0, 3, 6, 9, 12, 15, 18, 21],
# >>  [0, 4, 8, 12, 16, 20, 24, 28]]




It looks like you might be coming from PHP or something. If that is the
case, you should know that PHP's Arrays are sort of a hybrid between arrays
and hash tables, filling both of those roles. In Ruby, they are different
classes. But in Ruby 1.9.x, Hashes are ordered as in PHP (though they won't
presume Array like indexing).

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